#1 TwoSum_leetcode

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//Brute force

class Solution1 {

public:
vector<int> twoSum(vector<int>& nums, int target) {
vector<int> res;
for(int i=0 ; i<nums.size(); i++)
for(int j=i+1; j<nums.size();j++){
if(nums[i]+nums[j]==target){
res.push_back(i);
res.push_back(j);
return res;
}
else
continue;
}
}

};

//hashtable

class Solution {
public:
vector<int> twoSum(vector<int> &numbers, int target) {
vector<int> result;
map<int, int> m;
if (numbers.size() < 2)
return result;
for (int i = 0; i < numbers.size(); i++)
m[numbers[i]] = i;

map<int, int>::iterator it;
for (int i = 0; i < numbers.size(); i++) {
if ((it = m.find(target - numbers[i])) != m.end())
{
if (i == it->second) continue;
result.push_back(i+1);
result.push_back(it->second+1);
return result;
}
}
return result;
}
};

class Solution {
public:
vector<int> twoSum(vector<int>& nums, int target) {
vector<int> res;
multimap<int, int> numsMap;
multimap<int, int>::iterator iter1;
int max = nums.size();

//数组转进map，用下标做键
for (int i = 0; i < max; i++)
{
numsMap.insert(pair<int, int>(nums[i], i + 1));
}

for (iter1 = numsMap.begin(); iter1 != numsMap.end(); iter1++){

//map.(target-a)存在，则存在a + b = target
//且不是本身。
if ((numsMap.end() != numsMap.find(target - iter1->first)) &&
((numsMap.find(target - iter1->first))->second)//第二个下标，即(target-a)
!= iter1->second)//第一个下标，即a
{
//将下标存到vector，并排序
res.push_back((iter1->second));
res.push_back((((numsMap.find(target - iter1->first))->second)));
sort(res.begin(), res.end());
break;
}
}

return res;

}
};

int main()
{
vector<int> nums = {0,2,4,0 };
Solution1 a;
cout << a.twoSum(nums, 0)[0] << " " << a.twoSum(nums, 0)[1] << endl;
return 0;
}

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